1. Field of the Invention
The present invention relates to a lens barrel used in a camera for example, and more particularly relates to the lens barrel with an optical system for preventing an image shake, or for correcting or compensating a deviation of an image-forming position, which is caused by a camera shaking or camera movement.
2. Description of the Related Arts
When a camera body is moved or shaken at time of photographing, an image-forming position or a position of object image, onto a photosensitive surface, is deviated out of position. In order to prevent such a deviation of the image-forming position, there have been proposed various types of photographic lenses provided with an optical system for correcting the deviation caused by such a shaking or movement of the camera body.
For example, Japanese Laid-Open Patent Publication No. 7-191361 discloses a photographing lens 1, as shown in FIG. 27, which includes a main photographic optical system 5, and an afocal lens group 3 consisting of a pair of lenses 3a and 3b, in front of the main photographic optical system 5, that function as an image shake preventing optical system 3. Generally, the afocal lens group points to a lens system which is constituted of at least two lenses each of which has a specified optical characteristic (i.e. a characteristic by which a light is converged or diverged, etc.), and which has no specific optical characteristic as a whole. According to the mechanism of the Publication, one lens 3a of the shake preventing optical system 3 is moved at a right angle with respect to an optical axis S and in a vertical direction V by a predetermined amount, and another lens 3b thereof is moved at a right angle with respect to the optical axis S and in a horizontal direction H by a predetermined amount, so as to correct the deviation of an image forming position relative to an optical system of the camera.
However, each of the driving mechanisms 4a and 4b requires a great driving force, is slow in its responding speed and has a complicated construction, because the lenses 3a and 3b are moved in parallel with each other by means of screws in the driving mechanisms 4a and 4b for driving the pair of lenses 3a and 3b of the image shake preventing optical system 3.
Also, the conventional mechanism requires a wide space approximately rectangular for accommodating the pair of driving mechanisms 4a and 4b therein, which in turn requires the lens barrel with a greater outer diameter.
In particular, in case that the shake preventing optical system 3 is positioned in front of the main photographing optical system 5, the outer diameters of the lenses 3a and 3b in the image shake preventing optical system 3 need to be greater than that of the lens in the main photographing optical system 5 in order to receive a bundle of rays which diverge. Thus, there is a constant growing demand for miniaturizing the driving mechanisms 4a and 4b as much as possible.
Also, according to the conventional mechanism, a guide bar and a driving motor are installed outside the supporting frames of the lenses 3a and 3b in the radial direction thereof. Thus, a wide space is required to accommodate the driving mechanisms 4a and 4b for moving the lenses 3a and 3b of the image shake preventing optical system 3 in parallel with each other, which in turn necessitates the lens barrel to be large in its outer diameter.
Also, according to the conventional mechanism, the lens supporting means which supports the lenses 3a and 3b in the shake preventing optical system 3 so that the lenses 3a and 3b are movable in parallel with each other, includes an engaging portion which engages a guide rod extending in a tangential direction from the lens frame of the lens 3a or 3b. Thus, a wide space is required to accommodate the guide rod and the engaging portion therein, which in turn causes a problem in which the outer diameter of the lens barrel can not help but be constructed larger.
Meanwhile, Japanese Laid-Open Patent Publication No. 7-28115 discloses a lens barrel, as shown in FIG. 30, in which a pair of image shake preventing lenses 1 are moved in two directions perpendicular to the optical axis thereof and moved in parallel with each other. According to the mechanism, a pair of screw shafts 4x and 4y which are perpendicular to each other are rotated to move themselves back and forth, respectively, so that the lens frames 3 of the image shake preventing lenses 1 are moved in parallel with each other through the movable members 3x and 3y. In the mechanism, a pair of springs 5x and 5y are mounted to bias the pair of screw shafts 4x and 4y so that a thrust shake of the screw shafts 4x and 4y, and a backlash between the engaging parts thereof are removed, and so that the movement of the screw shafts 4x and 4y is transmitted to the lens frame 3 for the image shake preventing lens 1 reliably.
However, because there are mounted the movable members 3x and 3y, the screw shafts 4x and 4y, and the urging springs 5x and 5y around the image shake preventing lenses 1, there arises a problem in which the outer diameter of the lens barrel is constructed necessarily large.